128 RESPIRATION 



a sort of vibration, producing the effect called fremitus, which may be 

 felt even with the ringer. Rarely there are in a cavity both air and 

 liquid, and we hear the sound arising from the shaking together of these 

 two sorts of fluids in a vessel (succussion). 



Anything which lessens the tone or elasticity of the lung-tissue pro- 

 longs expiration, this process being one of passive recoil. Such a con- 

 dition obtains in emphysema. When the contiguous surfaces of the 

 pleura (the pulmonary and the costal) , instead of being very smooth and 

 well lubricated, are covered more or less with exudated solid materials, 

 there is friction which gives rise to easily heard and characteristic sounds. 

 This happens often in pleurisy and in tuberculosis. Sometimes, as in 

 pneu mo thorax, for example, the conditions in the lungs are such that 

 drops of liquid fall into a cavity. Then there is a peculiar sound known 

 often as metallic tinkling. It may be produced by drops of secretion 

 falling from the end of a bronchus into a cavity. 



Some Respiratory Quantities. The capacity of the lungs and the rela- 

 tions of the various volumes of air and of gases remaining and passing 

 in and out under various circumstances have a certain interest and 

 importance both theroretically and therapeutically as well as for the 

 purposes of athletic measurement. The first of these that we need to 

 consider is the tidal air. This is that volume of air which goes out and 

 in at every breath. On the average in the adult man its quantity is 

 about 500 c.c., or about 7 c.c. per kilo of body-weight. Perhaps the 

 most noteworthy fact about the tidal air is its small amount compared 

 with the lung-capacity, for only about 15 per cent, of the air in the 

 lungs under normal conditions passes out at each breath. This fraction 

 is called the co-efficient of ventilation. The vital capacity of any indi- 

 vidual is the volume of air he can, by the greatest effort, expire after 

 the most complete inspiration. A more accurate term for this quantity 

 would be respiratory capacity, its importance to life being somewhat 

 less than the inventor of the term "vital capacity" supposed. Vierordt 

 states that for man on the average it is 3400 c.c., and for woman 2500 

 c.c., a marked and important sexual difference. These quantities, 

 however, may be raised a good deal by practice and by general athletic 

 training, especially by running. This shows probably that the muscles 

 of the bronchioles may be developed by exercising them, so that more 

 air than before can enter the alveoli. 



Other respiratory quantities are the so-called supplemental air, the 

 complemental air, the stationary air, the residual air, the bronchial 

 capacity, the alveolar capacity, and the lung-capacity. What these are 

 in general can be made out from their names. 



The Respiration of the Fetus. Unlike the circulatory organs, the 

 fetal mechanism of respiration does not begin its work until after birth, 

 when for the first time it can have air with which to inflate the lungs. 

 The fetus, however, breathes, but oxygen and not air, and it excretes 

 the carbon dioxide, inevitable product of its tissue-metabolism, into the 

 maternal blood instead of into the atmosphere. Fetal respiration, then, 



